1. Field of the Disclosure
This disclosure relates generally to oilfield downhole tools and more particularly to modular drilling assemblies utilized for directionally drilling wellbores.
2. Description of the Related Art
To obtain hydrocarbons such as oil and gas, boreholes or wellbores are drilled by rotating a drill bit attached to the bottom of a drilling assembly (also referred to herein as a “Bottom Hole Assembly” or “BHA”). The drilling assembly is attached to the bottom of a tubing, which is usually either a jointed rigid pipe or a relatively flexible spoolable tubing commonly referred to in the art as “coiled tubing.” The string, which includes the tubing and the drilling assembly, is usually referred to as the “drill string.” When jointed pipe is utilized as the tubing, the drill bit is rotated by rotating the jointed pipe from the surface and/or by a mud motor contained in the drilling assembly. In the case of a coiled tubing, the drill bit is rotated by the mud motor. During drilling, a drilling fluid (also referred to as “mud”) is supplied under pressure into the tubing. The drilling fluid passes through the drilling assembly and then discharges at the drill bit bottom. The drilling fluid provides lubrication to the drill bit and carries to the surface rock pieces disintegrated by the drill bit in drilling the wellbore. The mud motor is rotated by the drilling fluid passing through the drilling assembly. A drive shaft connected to the motor and the drill bit rotates the drill bit.
A substantial proportion of current drilling activity involves drilling deviated and horizontal wellbores to more fully exploit hydrocarbon reservoirs. Such boreholes can have relatively complex well profiles. To drill such complex boreholes, some drilling assemblies utilize a plurality of independently operable pads to apply force on the wellbore wall during drilling of the wellbore to maintain the drill bit along a prescribed path and to alter the drilling direction. For rotating drill stings, such pads may be positioned on a non-rotating sleeve disposed around the rotating drive shaft. These pads are moved radially to apply force on the wellbore in order to guide the drill bit and/or to change the drilling direction outward by electrical devices or electro-hydraulic devices.
The present disclosure addresses the certain other apparatus and methods for steering a drill bit.